A wireless power transmission technology is known as a technology which uses the magnetic coupling between a primary (power feeding) coil and a secondary (power receiving) coil which face each other and transmits the energy of an alternate current applied to the primary coil to the secondary coil wirelessly.
In this wireless power transmission technology, when the state of the magnetic coupling between the primary coil and the secondary coil or the load state changes, the output of the rectifier falls into an unstable state. Thereby, it is necessary to control the output of the rectifier to a predetermined voltage, current, or power so as not to surpass the workable range of the element of the output stage. However, for the stable control of the output of the rectifier, it is necessary to monitor the state of the power receiving side at the power feeding side, but in the wireless power transmission technology, there is a problem that the state of the power receiving side cannot be monitored by a wired communication means since the power feeding side unit and the power receiving side unit are physically separated from each other.
In order to solve such a problem, for example, Patent Document 1 discloses a power transmission system including a power feeding device having a power feeding side controlling device for controlling an AC converter, and a power receiving device provided with a measuring communication device which measures the output voltage and the output current of a rectifier and transmits the measured results to the power feeding side controlling device, wherein, the power feeding side controlling device controls the AC converter to obtain a desired values of output voltage and output current of the rectifier based on the measured results of the output voltage and the output current of the rectifier received from the measuring communication device.